Remove obsolete _EXPORT macro not used under Win32.

This was a leftover from bad old Win16 days.

src/msw/dde.cpp

@@ -65,14 +65,15 @@ static wxDDEConnection *DDEFindConnection(HCONV hConv);
 static void DDEDeleteConnection(HCONV hConv);
 static wxDDEServer *DDEFindServer(const wxString& s);
 
-extern "C" HDDEDATA EXPENTRY _EXPORT _DDECallback(WORD wType,
-                                                  WORD wFmt,
-                                                  HCONV hConv,
-                                                  HSZ hsz1,
-                                                  HSZ hsz2,
-                                                  HDDEDATA hData,
-                                                  DWORD lData1,
-                                                  DWORD lData2);
+extern "C" HDDEDATA EXPENTRY
+_DDECallback(WORD wType,
+             WORD wFmt,
+             HCONV hConv,
+             HSZ hsz1,
+             HSZ hsz2,
+             HDDEDATA hData,
+             DWORD lData1,
+             DWORD lData2);
 
 // Add topic name to atom table before using in conversations
 static HSZ DDEAddAtom(const wxString& string);
@@ -771,7 +772,7 @@ bool wxDDEConnection::DoAdvise(const wxString& item,
 
 #define DDERETURN HDDEDATA
 
-HDDEDATA EXPENTRY _EXPORT
+HDDEDATA EXPENTRY
 _DDECallback(WORD wType,
              WORD wFmt,
              HCONV hConv,